Current and voltage controlled battery charger

ABSTRACT

Battery charging method and apparatus for performing the method including a controlled rectifier and a trigger circuit in which a current transformer senses charging current, a voltage divider senses battery terminal voltage, and signals developed from both of the current and voltage sensing devices are used to control the operation of the trigger circuit. Current control is maintained during initial portion of the charging cycle with voltage control being substituted to diminish charging current after which a second current control maintains a closely controlled &#39;&#39;&#39;&#39;trickle&#39;&#39;&#39;&#39; charge level. The three control modes operate sequentially, all use the same common reference value and all control the same charging circuit valve. A second embodiment of the apparatus uses two controlled rectifiers, fired alternately.

[ CURRENT AND VOLTAGE CONTROLLED BATTERY CHARGER 7'51 Inventor: Lewis A.M'diar, Or ela nd, P5.

[73] Assignee: Foilroducts Company,

Philadelphia, Pa.

[22] Filed: Oct. 4, 1971 [21] Appl. No.: 186,354

Related US. Application Data [63] Continuation of Ser. No. 768,684, Oct.18, 1968.

[56] I References Cited UNITED STATES PATENTS 3,517,295 1/1970 Lapuyade320/39 X FOREIGN PATENTS OR APPLICATIONS 11/1962 France 1451 Sept. 11,1973 Primary Examin z:r.1. D. Miller Assistant Examiner-Robert J. HickeyAtto'rneyRoylance, Abrams, Berdo & Kaul [57] ABSTRACT Battery chargingmethod and apparatus for performing the method including a controlledrectifier and a trigger circuit in which a current transformer sensescharging current, a voltage divider senses battery terminal voltage, andsignals developed from both of the current and voltage sensing devicesare used to control the operation of the trigger circuit. Currentcontrol is maintained during initial portion of the charging cycle withvoltage control being substituted to diminish charging current afterwhich a second current control maintains a closely controlled tricklecharge level. The three control modes operate sequentially, all use thesame common reference value and all control the same charging circuitvalve. A second embodiment of the ap- CURRENT AND VOLTAGE CONTROLLEDBATTERY CHARGER This is a continuation of application Ser, No. 768,684filed Oct. 18, 1968 now abandoned. I

This invention relates to battery charging apparatus, and morespecifically to a method and apparatus for charging one or more electricstorage batteries with a controlled current-voltage profile.

The fundamental problem of storing energy in an electrochemical cell is,fundamentally, one of passing a suitable charging current through thecell in the proper direction to reverse the chemical reaction therein.Many prior art workers have attacked this problem with varying degreesof success. Since the ad- -vent of the controlled rectifier, andespecially since the charging problems because the ampere-time productof I the charge supplied can be accurately controlled by rendering thecontrolled rectifier conductive at a precisely controllable point ineach cycle of the full-wave or half-wave rectified supply current.

However, along with the advantages a number of disadvantages andproblems have appeared in controlled rectifier circuits, primarily theproblems of protecting the controlledrectifier from excessive currentswhich would render even thelarger controlled rectifiers useless. This isespecially true when the charger is connected to a fully dischargedbattery or is short circuited. There are, of course, practical limits incost, size and availability to the current capacity of the controlledrectifier to be used.

In addition, the use of a controlled rectifier in a battery chargingcircuit presents the challenges of developing a circuit which cancontrol the rectifier in various modes to automatically provide chargingcurrent to the battery at different levels in the same charging cycle.,

An object of the present invention is to provide a bat tery chargingcircuitusing .a controlled rectifier in which the charging current islimitedto safe levels.

Another object is to provide a method of charging a batteryin whichthree types or formsof control are provided in sequence, the three typesbeing high cur-- rent, voltage and low current.

Another object is to provide a charging circuit in which a controlledrectifier is rendered conductive by trigger pulses from a controlcircuit which'responds to both battery charging current and batteryterminal voltage. 7 I

Yet another object is to provide a charging circuit in which the chargecurrent profile follows a preselected pattern which adapts itself to theneeds of an individual battery or group of batteries.

A further object is to provide anapparatus in which charging current isdirectly sensed and is used to limit the ampere-time product which thecontrolled rectifier is allowed to provide to the battery.

are provided. Each type of control is mutually contradictory to theother two, yet each type dominates during its portion of the chargingsequence without conflict from the other controls. The three controlsall operate from a common reference value and all control via the sameelement.

The invention also includes a novel apparatus having semiconductorcontrol and sensing elements. The control systems provide a first periodwherein the charging current is held constant while the battery terminalvoltage rises to a predetermined voltage level. The second controlperiod begins when that predetermined voltage is attained. The secondcontrol'system'maintains the voltage level constant while the chargingcurrent diminishes to a predetermined lower level. The third controlsystem maintains the charging current constant at the lower level forthe remainder of the charge. The transfer of control dominance fromsystem to system is accomplished without mechanical switching or timers.

In order that the manner in which the foregoing and other objects areattained in accordance with the invention can be understood in detail, aparticularly advantageous embodiment thereof will be described withreference to the accompanying drawings, which form a part of thespecification, and wherein:

FIG. l is a schematic diagram of one embodiment of an apparatus inaccordance with the invention;

FIG. 2 is a current-voltage curve showing a typical profile of thecharging pattern which can be accomplished with the apparatus of FIG. 1;and

FIG. 3 is a schematic diagram of another embodiment of an apparatus inaccordance with the invention.

Referring now to FIG. 1, a source of AC voltage is connected to thepower input portion of the circuit at terminals 1 and 2, the terminalsbeing connected to the primary winding 3 ofa conventional powertransformer indicated generally at 4. The circuit portion betweenterminal 1 and winding 3 includes a normally closed switch 5 which isactuated by a timer motor 6. The timer motor serves the function ofterminating. the charging process a preselected period of time after thecharging process has progressed through a portion of its cycle as willbe described hereinafter. Timer motor 6 is'connected across the AC lineon the primary side and is energized by a single-pole, double-throwcontact set indicated generally at 7. In the position of contact set 7wherein the timer motor is not energized, the contact set provides acomplete circuit for an indicator lamp 8 which is connected across theAC supply and which is included to indicate to an operator that theapparatus is in the early phases of the charging cycle. A fan 9 is alsoconnected across the AC power source to provide cooling for variouscomponents in the apparatus.

A secondary winding l0 of transformer 4 includes two end terminals and acenter tap, the center tap being connected to the cathode of aconventional controlled rectifier 11. The anode of rectifier'll' isconnected to a suitable connector device 12, such as a conventionalbattery clamp, which can be attached to the negative terminal of thebattery or batteries 13 to be charged. The positive terminal of thebattery is connected to a similar connector 14 which is connectedthrough a conventional ammeter l5 and circuit breaker 16 to the cathodeelectrodes of two rectifiers l7 and 18. The anode electrode of rectifier17 is connected via a conductor 19 to one end terminal of secondarywinding 10 of transformer 4. The anode electrode of diode 18 issimilarly connected via a conductor to the other end terminal ofsecondary winding 10.

As schematically shown in FIG. 1, conductors 19 and 20 pass through andare inductively coupled to a permeable core 21 which is designed todevelop flux with relatively low magnetomotive force and to saturate atlow levels of current carried by conductors 19 and 20. It will be seenfrom FIG. 1 that conductors 19 and 20 pass through core 21"in oppositedirections so that the magnetomotive force (MMF) produced in core 21 bythe current through conductor 19 and the MMF produced by the currentflowing in conductor 20 are effective to reconstruct an AC signal in asecondary winding 35. Winding 35 is a center-tapped winding on core 21and is connected to control circuitry to be described hereafter. Becauseof rectifiers 17 and 18, the currents flowing in conductors l9 and 20are pulsating DC and are 180 out of phase because they are connected tothe end terminals of a center-tapped secondary windmg.

The unidirectional pulsating current in conductor 19 produces an M MF inone direction during one half cycle of the AC appearing in secondarywinding 10. The current in conductor 20 produces an MMF in the otherdirection during the other half cycle. To secondary winding 35, thisalternating force appears to be the result of an AC signal applied to aprimary winding and an AC signal is developed in winding 35. Thedifference between the MMFs in core 21 produce current in winding 35representative of the magnitude of the total charging current flowingthrough conductors 19 and 20.

The alternating current from the secondary winding is rectified bydiodes 17 and 18 and provided to the battery whenevercontrolledirectifier 11 is rendered conductive. The gate electrode ofrectifier 11 is connected to the base 1 electrode of a conventionalunijunction trasistor (UJT) indicated generally at 25. A resistor 26 isconnected between the base 1 electrode and ground. The base 2 electrodeis connected through a resistor 27 to the cathode electrode of aconventional Zener diode 28, the anode electrode of which is connectedto ground. The cathode electrode of diode 28 is also connected through aresistor 32 to positive battery connector 14.

The emitter'electrode of UJT is connected to one terminal, of a resistor29, to one terminal of a resistor 30 and to one terminal of acapacitor'3l. The other terminals of resistor 30 and capacitor 31 areconnected to ground andthe other terminal of resistor 29 is connected toa source of charging current for capacitor 31, to be describedhereafter. Resistor 29 and capacitor 31 form an RC timing circuit forUJT 25 in a manner which is well known in the art.

Secondary winding 35 is wound around core 21 and is provided with twoend terminals and a center tap, the center tap being connected toconnector 14 at the positive battery terminal. One end terminal isconnected to the cathode electrode of a conventional semiconductor diode36 and the other end terminal is connected to the cathode electrode of aconventional diode 37. The anode electrodes of the two diodesareconnected to each other and to a conventional filter circuit including aseries resistor 38 and two capacitors 39 and 40 which are connectedbetween the two ends of resistor 38 and the positive battery and chargerterminal. A voltage divider circuit is connected between the output ofthe filter circuit and the center tap of winding 35, the voltage dividerincluding a fixed resistor 41, the resistance element of a potentiometer42, a fixed resistor 43 and the resistance element of a potentiometer44. As will be recognized by those skilled in the art, the fluxgenerated in core 21 by the charging current produces a current inwinding 35 which is rectified by diodes 36 and 37, filtered, andconducted through the four resistors in the voltage divider, producingvoltages at various points in the divider, the variations in each ofwhich is representative of changes in magnitude of charging current. Theresistance element of a potentiometer 45 is connected in parallelcircuit relationship with resistors 41 and 43 and with the resistanceelement of potentiometer 42 to provide an additional point at which asignal representative of charging current can be obtained. The movablecontact of potentiometer 45 is connected through a fixed resistor 46 tothe base electrode of a conventional NPN transistor indicated generallyat 47. The collector electrode of transistor 47 is connected to the baseelectrode of a conventional PNP transistor indicated generally at 48. Acapacitor 49 is connected between the collector electrode of transistor47 and one terminal of a fixed resistor 50 which is also connected toone terminal of the energizing winding of an electromagnetic relay 51.The other terminal of resistor 50 is connected to the collectorelectrode of transistor 48, the emitter electrode of which is connectedto the junction between a fixed resistor 52 and a fixed resistor 53which are connected in' series circuit relationship with a fixedresistor 54 between the positive battery and charger terminal and areference voltage circuit. The emitter electrode of transistor 47 isconnected at the junction between resistors 53 and 54.

Transistors and 48 and the associated circuitry described aboveconstitute a current level sensing circuit 55, the purpose of which isto respond to a preselected level of diminishing charging current, asrepresented by the voltage at the movable contactor of potentiometer 45,and to provide energizing current to relay 51 when that current level isreached. Energization of relay 51 then moves the movable contact ofcontact set 7 from the position shown in FIG. 1 to the position in whichthe timer motor is energized. The timer then begins toooperate and,after the selected time period for which the timer is designed, contact5 is opened, deenergizing the entire apparatus.

The cathode electrode of a Zener diode 56 is connected to the positivebattery terminal and charger connector 14. The anode electrode of diode56 is connected to one terminal of a fixed resistor 57, the otherterminal of which is connected to the other terminal of r'elay5l and tothe cathode electrode of a Zener diode 58. The junction between diode 56and resistor 57 is connected to the other end of the series circuitincluding resistors 52, 53 and 54.

The series circuit including Zener diodes 56 and 58 andresistor 57 formsone leg of a bridge circuit which is connected in parallel circuitrelationship with the battery when a battery is attached to connectors12 and 14. The other leg of the bridge is formed by a series cirof apotentiometer, the movable contact of which is connected through a diode64 to the base electrode of a conventional NPN transistor indicatedgenerally at 65. The emitter electrode of transistor 65 is connected tothe junction between diode 56 and resistor 57 in the opposite leg of thebridge. Thus, the base-emitter circuit of transistor 65 and diode 64 areconnected across the two corners of the bridge to detect an unbalancebetween these two points, the movable contact of potentiometer 62constituting the corner of the bridge in the leg including the fourseries resistors.

A capacitor 66 is connected between the base electrode and the collectorelectrode of transistor 65, the collector electrode being connectedthrough a resistor 67 to the base electrode of a conventional'PNPtransistor indicated generally at 68. The base electrode of transistor68 is connected through a fixed resistor 69 to the emitter electrode ofthat transistor and to the movable contact of potentiometer 42. Thecollector electrode of transistor 68 is connected through fixed resistor29 to the emitter electrode of UJT 25, the emittercollector circuit oftransistor 68 constituting the current supply for the timing circuit totrigger the UJT.

A conventional semiconductor diode 70 and a fixed resistor 71 areconnected in series circuit relationship between the base electrode oftransistor 65 and the movable contact of potentiometer 44 in the currentsignal voltage divider.

Transistors 65 and 68 and-the associated circuit elements constitute theprimary voltage and current control means for the UJT trigger circuitwhich, in turn, controls SCR ll. Transistor 68 can be referred to as thecurrent control transistor because its primary function is to controlthe triggering of the SCR during the controlled current portions of thecharging profile. Transistor 65 can be referred to as the voltagecontrol transistor because its primary function is to control thevoltage across the battery terminals during a different portion of thecharging profile. This latter terminology is not totally accuratebecause both transistors. are actually used in both current and voltagecontrol. However, this terminology is convenient for discussionpurposes.

It may be helpful in considering the operation of the apparatus toregard the circuit including transistors 65 and 68 as a form of NORlogic circuit, a connection of the two elements in series, oneelement(transistor 65) being responsive to battery voltage and the other(transistor 68) to charging current. The series connection is thebase-emitter circuit of transistor 68 in series with thecollector-emitter circuit of transistor 65. This circuit is an importantpart of the apparatus because it allows the three step, or three mode,control to operate without undesirable conflict between modes.

To discuss the operation ofthe above circuit, it will be convenient torefer to the current-voltage curve shown in FIG. 2 wherein the ordinaterepresents charging current supplied to the battery and the abcissarepresents the terminal voltage of the battery. It will be assumed thatthe charging process commences with the battery largely discharged. Inthis case it is desirable to charge the battery at a relatively highcurrent level and to continue the high current level until the batterytertrol at a voltage near the final voltage to which the battery is tobe charged, the charging cycle is changed from the current control whichexisted in portion A-B to a voltage control wherein the charging currentis allowed to vary but the terminal voltage of the battery is maintainedrelatively constant, this being illustrated by the region B-C. At pointC the battery has nearly reached the desired terminal voltage and thecontrol mode is again changed to current control, but this time at asubstantially lower'level than during the portion A-B.

It will also be noted that the portion B-C exhibits a slight negative"slope wherein the voltage decreases slightly as current decreases undervoltage control. This is simply due to charges in the operating pointsof the transistors in the circuit. No instabilityis introduced becausethe control is based on voltage and the current cannot jump between thedouble value points.

The low charging current control takes over rather abruptly when thecharging current diminishes to the preselected level, and the lowcharging current is thereafter very closely controlled. It will be seenthat the control during this portion of the charging cycle is similar tothat during portion A-B but is actually more closely controlled becauseof the effective addition of another stage of gain in the controlcircuit. The low level charging current is allowed to flow until apreselected period of time has elapsed at which time the system isdeenergized at point D. The timing function is commenced, in theembodiment disclosed in FIG. 1, at a current level within the voltagecontrol region B-C which can be, for example, at point E. Thus, if abattery is connected to connectors 12 and 14 with a terminal voltagehigher than the flat" battery which was assumed to exist a point A, thesystem can adapt by providing high charging current for a relativelyshort time constituting only a portion of the A-B section at which timethe charging mode becomes voltage controlled and the timing sequencebegins. Portion A-B can, however, exist for as long as necessary tobring the battery or batteries up to a desired level of charge. This isespecially advantageous if many batteries are to be connected inparallel wherein the high charging current level would be needed for alonger period of time than for a single battery being charged.

One would normally expect that to obtain control of the type describedit would be necessary to provide separate controls and referencevoltages and complicated interlocks to prevent the operation of one partof the control system fromworking against another porv tion of thecircuit. This conflict is entirely avoided by the novel circuitdescribed above.

A charging profile such as that shown in FIG. 2 can be attained with theapparatus of FIG. 1, as fol-lows. Initially the current flow throughconductors l9 and 20 is relatively large and the voltage produced bysecondary winding 35 across series resistors 41-44 is similarly large.The center tap of winding 35 is maintained at the positive voltage levelof the positive battery terminal and the voltage drop across the seriescircuit including the resistance elements of potentiometers 44 and 45 isrelatively large, maintaining the anode electrodes of diodes 36 and 37at a relatively large negative level compared to the positive batteryterminal. The movable contact of potentiometer 45 is therefore alsomaintained at a negative level. The emitter electrode of transistor 47is held at a relatively constant level by the regulating action of Zenerdiode 56, the value thereof being selected to keep the emitter electrodemore positive than the base electrode. Transistor 47 and transistor 48are therefore maintained in a substantially nonconducting conditionthroughout the high charge current portion of the cycle represented bythe section A-B of FIG. 2.

However, as thecharging current decreases to point E the potential atthe movable contact of potentiometer 45 and, accordingly, at the baseelectrode of transistor 47 increases, rendering transistor 47 conductiveand placing transistor 48 in a conductive state.

Thecircuit including transistors 47 and 48 is essentially a bistablecircuit. When transistor 47 begins to conduct its emitter-collectorcurrent is amplified by transistor 48. The emitter-collector current oftransistor 48 is fed through resistor 52 as positive feedback totransistor 47, driving it further into conduction. By this regenerativeaction the circuit is driven into the conductive state very quickly,resulting in a snap action which provides energizing current throughresistor 50 to the energizing winding of relay 51, thus activating thatrelay. The movable contact of contact set 7 is then switched to theother position from that shown in FIG. 1, providing energizing voltagefor timer motor 6 which commences the timing cycle to terminate at pointD of FIG. 2.

While circuit 55 is relatively inactive during the high charging currentportion of the cycle, transistors 65 and 68 are active. While highcharging current flows, the voltage developed at the movable contact ofpotentiometer 42 is somewhat below the terminal voltage at connector 14.The emitter electrode of transistor 65 is held at a substantiallyconstant level relative to connector 14 by Zener diode 56 in one leg ofthe bridge circuit, while the base electrode of transistor 65, throughdiode 64, responds to variations of voltage at the movable contact ofpotentiometer 62. The base voltage is of a comparable magnitude to thevoltage of diode 56 and is determined by the resistors in the seriesvoltage divider circuit constituting that portion of the bridge. Thecurrent flow through the emitter-collector circuit of transistor 65 isat full saturation level, resulting in very low emittencollectorvoltage. Transistor 65 is, effectively shorted outIThe current throughresistors 67 and 69 maintains the base electrode of transistor 68 at aslightly less positive'level than the emitter electrode, permittinglimited and controlled current flow through the emitter-collectorcircuit of transistor 68 to resistor 29 and to capacitor 31. Astheeharging current tends to increase the movable contact ofpotentiometer 42 becomes more negative, driving the emitter electrode oftransistor 68 more negative and diminishing conduction, therebyproviding decreased charging current through resistor 29 to capacitor3l. As will be apparent to those skilled in the art, the frequency withwhich UJT 25 is allowed to conduct depends upon the resistance value ofresistor 29, the value of capacitor 31, the I A-B of FIG. 2 transistor68 maintains close control over the frequency of firing of.UJT 25 and,consequently, of controlled rectifier 11. If the current tends toincrease beyond the preselected safe level, the charging current isdecreased, delaying the firing of UJT 25 and, therefore, of SCR II. Thisautomatically decreases the charging current to a desired level. It willbe observed that the voltage control (transistor 65) is essentiallycalling for full current in an effort to take the voltage up to thevoltage control point. However, the baseemitter circuit of transistor 68senses current and, because of the series NOR circuit control, overridesthe voltage sensing and provides current control.

When the batteryterminal voltage increases sufficiently to commence thecontrolled voltage portion of the cycle, the voltage drop across theentire bridge circuit increases because the bridge circuit is directlytied to the battery terminals. The voltage drop across the voltagedivider including resistors -63 causes the base electrode of transistorto decrease, decreasing the conduction of transistor 65 and accordinglydecreasing the base current of transistor 68.

This commences the voltage control portion of the cycle with transistor65 sensing the variation across divider 60-63 at the movable contact ofpotentiometer 62 as compared with the reference voltage provided bydiode 56. During this mode the emitter-base potential of transistor 68is no longer controlling; instead, transistor 68 is controlled by itsemitter-base current which is now controlled by transistor 65.

As battery voltage rises, transistor 65 is rendered less and lessconductive, gradually reducing charging current. If this procedure wereallowed to proceed unimpeded, the net effect would be to reduce tonothing the charging current at point C. However, a second currentcontrol comprising the series circuit including diode 70 and resistor 71begins to conduct current when the charging current diminishes due tothe increase of voltage at the movable contact of potentiometer 44. Atlow charging current levels this circuit maintains transistor 65sufficiently conductive to provide a current to bias transistor 68 in aslightly conductive condition, maintaining a small charging current forcapacitor 31 and, hence, relatively late trigger pulses from UJT 25 forcontrolled rectifier 11. This constitutes a third control circuit whichmaintains a charge current at a low, preset controlled level. The levelof this finish" charge current is substantially independent of linevoltage variations or battery terminal voltage variations within thedrive limitations of the charger. The control exercised during thefinish charge period is similar to that of the high current control butat a lower level and with increased sensitivity. The increasedsensitivity and improved control at the low level is due to theeffective addition of transistor 65 as an additional stage of gain.During the high current portion, transistor 65 was in saturation andprovided only a current path. However, in portion C-D,'transistor 65responds to base voltage changes and amplifies them, thus providing theadditional gain.

Timer motor 6 is started by relay 5], as previously described, near theend of the controlled voltage portion of the cycle. Clearly, the circuitcontrolling relay 51 could be set to operate at any current level.However, to avoid early termination of the finish charge, the circuit isadvantageously 'set to operate at a current level slightly greater thanthe finish charge current. The finish-charge current control thereforeprovides a low charging current to battery 13 until timer motor 6completes its cycle at which time the system is deactivated by openingswitch 5. It is believed to be well understood in the art how theunijunction transistor and controlled rectifier circuit operate inproviding activating pulses during the positive half-cycles of thesupply voltage, rendering the controlled rectifier conductive for theremainder of each half-cycle. For a further discussion of this operationreference is made to the General Electric SCR Manual, 4th Edition, 1967,and especially to pages 76 and 163.

Zener diode 58 is included in the circuit to allow the SCR to turn offunder certain operating conditions. Without diode 58, when the chargeris connected to a flat" battery, one which is completely discharged, themagnitude of the current carried by SCR lll'during each cycle offull-cycle conduction is so great that there is not enough time betweenthe end of one conduction cycle and the beginning of the next for thecarriers to recombine. The SCR can, under these conditions, lose controland remain in conduction, leading to destruction of the SCR and possibledamage to other parts of the equipment. However, Zener diode 58 providesa low level cutoff to terminate conduction of the control circuitincluding transistors 65 and 68 and, hence, the SCR.

FIG. 3 shows a modified apparatus in accordance with the inventionwherein the single controlled rectifier is replaced by two controlledrectifiers and other modifications are made accordingly. The use of twocontrolled rectifiers allows the use of smaller devices and improves theswitching characteristics thereof.

The control circuit including transistors 47, 48, 65 and 68, and theassociated circuitry is substantially the same as in FIG. 1 and theinterconnections and operation thereof will not be described again indetail. It should be observed that Zener diode 58 of FIG. 1 no longerappears in the circuit of FIG. 3. This diode is no longer necessarysince the controlled rectifiers in the embodiment of FIG. 3 no longerfire on every. half cycle as was the case with the circuit of FIG. 1.The turn-off difficulty encountered with the single controlled rectifieris thereby eliminated. It will also be observed that the circuit of FIG.3 includes a capacitor 75 connected in parallel circuit relationshipwith resistor 32. This addition is included because of the phase shiftintroduced anode electrodesoftwo similar controlled rectifiers 83 and84. The cathode electrodes of rectifiers 83 and 84 are connected to theend terminals of the secondary winding of transformer 80, the conductorsbetween the controlled rectifiers and the transformer passing throughthe core of a current transformer 79 which performs the same function astransformer 21 described 'with reference to FIG. 1. The control circuitis connected, as in FIG. 1, to the secondary winding of the currenttransformer and to the positive and negative battery terminals.

Diodes 85 and 86 are connected between the cathode electrodes ofcontrolled rectifiers 83 and 84, re-' spectively, and the primarywinding of transformer 90. In effect, diodes 85 and 86 are inparallelwith the controlled rectifiers to bypass power around therectifiers W to the trigger circuits from transformer 80. The gateelectrode of rectifier 83 is connected to one terminal cated generallyat 90. The gate electrode of rectifier 84 is connected to a secondarywinding 88 of transformer 90, the other terminals of the two secondarywindings being connected to the cathode electrodes of the respectiverectifiers. A primary winding 89 is connected between the base 1electrode of a unijunction transistor 25 and ground. UJT 25 and thecircuit for its control is the same as that described with reference toFIG. I except for the modifications discussed above.

It will be observed that the two controlled rectifiers 83 and 84 replacediodes l7 and 18 of FIG. 1 and also controlled rectifier 11 of FIG. 1.Pulse transformer 90 provides pulses to the gate electrodes of bothcontrolled rectifiers on each half cycle of the energizing current, thetime within each half cycle at which the trigger pulse is supplied beingdetermined by the control circuit. However, only one of the controlledrectifiers conducts on each half cycle because the cathodes of thecontrolled rectifiers are provided with alternating current and, as iswell understood in the art, the gate-cathode relationship is suitablefor conduction by only one of the rectifiers at any given time.

While one advantageous embodiment has been chosen to illustrate theinvention, it will be understood by those skilled in the art thatvarious changes and modifications can be made therein without departingfrom the scope of the invention as defined in the appended claims.

What is claimed is:

1. A battery charging apparatus comprising the combination of first andsecond connector means connectable to the positive and negativeterminals of a battery to be charged for conducting charging current tothe battery;

a source of AC power including a power transformer having a secondarywinding with a center tap and two end terminals; a full wave rectifier;circuit means for connecting said source of AC power to said full waverectifier; i said circuit means including first and second conductors,one end of each conductor being connected to one end terminal of saidsecondary winding and the other end being connected to said rectifier; asemiconductor switching device connected to one of said connector meansand to said AC source,

said switch means having a control electrode and a switchable conductivepath connected in series with the battery when the battery is connectedto said connectors for controllably providing charging current to saidbattery; a current transformer having a magnetically permeablecoreinductively coupled to said circuit means, said current transformerhaving a secondary winding for providing a current representative of themagnitude of charging current in said circuit means,

said first and second conductors being magnetically coupled to said coreto constitute a primary winding,

said conductors being coupled to said core in directions to produce amagnetomotive force suitable vice for providing control signals to saidswitching V device in response to terminal voltage of, and chargingcurrent to, the battery. 2. Apparatus according to claim 1 wherein saidcontrol circuit means comprises rectifier circuit means connected tosaid secondary winding of said current transformer for providing arectified signal proportional in magnitude to the charging currentflowing through said first and second conductors;

a voltage divider connected to said connector means in parallel circuitrelationship with the battery being charged; and

semiconductor circuit means connected to said rectifier circuit meansand to an intermediate point on said voltage divider for providing acontrol current related to battery terminal voltage and to chargingcurrent; and

gate circuit means responsive to said control current for providingspaced energizing signals to the control electrode of said semiconductorswitching device.

3. A battery charging apparatus comprising the combination of first andsecond connector means connectable to the positive and negativeterminals of a battery to be charged for conducting charging current tothe battery;

a source of AC power;

a full wave rectifier;

circuit means for connecting said source of AC power to said full waverectifier, said circuit means connecting said source of AC power to saidfull wave rectifier carries charging current to the battery and iscoupled to said current transformer as a primary winding;

a semiconductor switching device connected to one of said connectormeans to said AC source, said switch means having a control electrodeand a switchable conductive path connected in series with the batterywhen the battery is connected to said connectors for controllablyproviding charging current to said battery;

a current transformer inductively coupled to said circuit means, saidcurrent transformer having a secondary winding for providing a currentproportional in magnitude of charging current in said circuit means; and

control circuit means connected to said secondary winding, to said firstand second connector means and to said control electrode of saidswitching device for providing control signals to said switching devicein response to terminal voltage of, and charging current to, thebattery,

said control circuit means including means connected to said secondarywinding for producing a unidirectional signal having a magnituderepresentative of the magnitude of the charging current,

means connected to said connector means for producing a unidirectionalsignal representative of battery terminal voltage,

means for producing a control current having a magnitude representativeof the chargingcurrent when battery terminal voltage is less than apreselected value; and

timing circuit means responsive to said control current for providingactivating signals to said control electrode of said semiconductorswitching device;

said timing circuit means comprising a unijunction transistor,

a capacitor connected between the emitter electrode and one baseelectrode, and

a resistor connected between said emitter electrode and said means forproducing a control current, said resistor, capacitor and transistorforming a relaxation timing circuit.

4. A battery charging apparatus comprising the combination of a sourceof AC power,

rectifier means for controlling the flow of pulsating unidirectionalcurrent;

connector means connectable to a battery to be charged for placing thebattery in circuit relationship with said rectifier means;

conductor means for interconnecting said AC source, said connector meansand said rectifier means in series circuit relationship;

a current transformer inductively coupled to said conductor means fordeveloping an electrical signal representative of the maginitude ofcurrent flowing in said conductor means;

divider circuit means connected to said connector means for developing asignal representative of battery terminal voltage; and

control circuit means connected to said current transformer, to saiddivider circuit means and to said rectifier means for providing spacedtrigger pulses to said rectifier means in response to said electricalsignals representative of current and battery terminal voltage toprovide limited high charging current to said battery until the terminalvoltage thereof reaches a preselected level, to provide an interval ofcontrolled voltage charging current, and to provide a low chargingcurrent thereafter.

5. Apparatus according to claim 4 wherein said rectifier means comprisesat least one thyristor connected in series circuit relationship withsaid AC source and said battery;

and said control circuit means comprises a trigger circuit for providingactivating pulses to said at least one thyristor.

6. Apparatus according to claim 4 wherein said control circuit meanscomprises a Zener diode connected to said connector means to provide areference voltage;

first transistor circuit means connected to said diode and to saiddivider circuit means for comparing battery terminal voltage with saidreference and for developing said signal representative thereof; and

second transistor circuit means connected to said first transistorcircuit means and to said current transformer for developing a signalrelated to charging current;

said first transistor circuit means being effective to inhibit operationof said second transistor circuit means when said battery terminalvoltage reaches tionship with said AC source and said battery;

a preselected level. and said control circuit means comprises 7.Apparatus according to claim 6 wherein a trigger circuit for providingactivating pulses to said said rectifier means comprises at least onethyristor. at least one thyristor connected in series circuit rela-

1. A battery charging apparatus comprising the combination of first andsecond connector means connectable to the positive and negativeterminals of a battery to be charged for conducting charging current tothe battery; a source of AC power including a power transformer having asecondary winding with a center tap and two end terminals; a full waverectifier; circuit means for connecting said source of AC power to saidfull wave rectifier; said circuit means including first and secondconductors, one end of each conductor being connected to one endterminal of said secondary winding and the other end being connected tosaid rectifier; a semiconductor switching device connected to one ofsaid connector means and to said AC source, said switch means having acontrol electrode and a switchable conductive path connected in serieswith the battery when the battery is connected to said connectors forcontrollably providing charging current to said battery; a currenttransformer having a magnetically permeable core inductively coupled tosaid circuit means, said current transformer having a secondary windingfor providing a current representative of the magnitude of chargingcurrent in said circuit means, said first and second conductors beingmagnetically coupled to said core to constitute a primary winding, saidconductors being coupled to said core in directions to produce amagnetomotive force suitable to provide in said secondary winding areconstructed AC signal when the currents in said conductors arepulsating and unidirectional and separated in phase by 180*; and controlcircuit means connected to said secondary winding, to said first andsecond connector means and to said control electrode of said switchingdevice for providing control signals to said switching device inresponse to terminal voltage of, and charging current to, the battery.2. Apparatus according to claim 1 wherein said control circuit meanscomprises rectifier circuit means connected to said secondary winding ofsaid current transformer for providing a rectified signal proportionalin magnitude to the charging current flowing through said first andsecond conductors; a voltage divider connected to said connector meansin parallel circuit relationship with the battery being charged; andsemiconductor circuit means connected to said rectifier circuit meansand to an intermediate point on said voltage divider for providing acontrol current related to battery terminal voltage and to chargingcurrent; and gate circuit means responsive to said control current forproviding spaced energizing signals to the control electrode of saidsemiconductor switching device.
 3. A battery charging apparatuscomprising the combination of first and second connector meansconnectable to the positive and negative terminals of a battery to becharged for conducting charging current to the battery; a source of ACpower; a full wave rectifier; circuit means for connecting said sourceof AC power to said full wave rectifier, said circuit means connectingsaid source of AC power to said full wave rectifier carries chargingcurrent to the battery and is coupled to said current transformer as aprimary winding; a semiconductor switching device connected to one ofsaid connector means to said AC source, said switch means having acontrol electrode and a switchable conductive path connected in serieswith the battery when the battery is connected to said connectors forcontrollably providing charging current to said battery; a currenttransformer inductively coupled to said circuit means, said currenttransformer having a secondary winding for providing a currentproportional in magnitude of charging current in said circuit means; andcontrol circuit means connected to said secondary winding, to said firstand second connector means and to said control electrode of saidswitching device for providing control signals to said switching devicein response to terminal voltage of, and charging current to, thebattery, said control circuit means including means connected to saidsecondary winding for producing a unidirectional signal having amagnitude representative of the magnitude of the charging current, meansconnected to said connector means for producing a unidirectional signalrepresentative of battery terminal voltage, means for producing acontrol current having a magnitude representative of the chargingcurrent when battery terminal voltage is less than a preselected value;and timing circuit means responsive to said control current forproviding activating signals to said control electrode of saidsemiconductor switching device; said timing circuit means comprising aunijunction transistor, a capacitor connected between the emitterelectrode and one base electrode, and a resistor connected between saidEmitter electrode and said means for producing a control current, saidresistor, capacitor and transistor forming a relaxation timing circuit.4. A battery charging apparatus comprising the combination of a sourceof AC power, rectifier means for controlling the flow of pulsatingunidirectional current; connector means connectable to a battery to becharged for placing the battery in circuit relationship with saidrectifier means; conductor means for interconnecting said AC source,said connector means and said rectifier means in series circuitrelationship; a current transformer inductively coupled to saidconductor means for developing an electrical signal representative ofthe maginitude of current flowing in said conductor means; dividercircuit means connected to said connector means for developing a signalrepresentative of battery terminal voltage; and control circuit meansconnected to said current transformer, to said divider circuit means andto said rectifier means for providing spaced trigger pulses to saidrectifier means in response to said electrical signals representative ofcurrent and battery terminal voltage to provide limited high chargingcurrent to said battery until the terminal voltage thereof reaches apreselected level, to provide an interval of controlled voltage chargingcurrent, and to provide a low charging current thereafter.
 5. Apparatusaccording to claim 4 wherein said rectifier means comprises at least onethyristor connected in series circuit relationship with said AC sourceand said battery; and said control circuit means comprises a triggercircuit for providing activating pulses to said at least one thyristor.6. Apparatus according to claim 4 wherein said control circuit meanscomprises a Zener diode connected to said connector means to provide areference voltage; first transistor circuit means connected to saiddiode and to said divider circuit means for comparing battery terminalvoltage with said reference and for developing said signalrepresentative thereof; and second transistor circuit means connected tosaid first transistor circuit means and to said current transformer fordeveloping a signal related to charging current; said first transistorcircuit means being effective to inhibit operation of said secondtransistor circuit means when said battery terminal voltage reaches apreselected level.
 7. Apparatus according to claim 6 wherein saidrectifier means comprises at least one thyristor connected in seriescircuit relationship with said AC source and said battery; and saidcontrol circuit means comprises a trigger circuit for providingactivating pulses to said at least one thyristor.